755
FXUS65 KPIH 041518
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
918 AM MDT Thu Sep 4 2025

.KEY MESSAGES...

- Cooler temperatures will starting returning to eastern Idaho

- Isolated thunderstorms possible today and Friday

- Better chance of rain and thunder expected this weekend

&&

.UPDATE...
Issued at 913 AM MDT Thu Sep 4 2025

We are doing a quick update this morning to tweak the potential
progression of isolated storms this afternoon through tonight.
We are still expecting a few storms in the central mountains
this afternoon, possibly spreading into the Snake Plain along
outflow boundaries. The higher resolution guidance is also
painting now what appears to be a convergence band/cold front
dropping south and west from out of Montana. We expanded the
footprint a bit more north and east based on that trend. It also
appears another surge of moisture moves just north of the Utah
border from around Oakley through southwest Wyoming. We should
see all of this gradually ending overnight, even though the
chance of a sprinkle or light shower remains at 10-15%. Anything
that forms won`t have much potential for rainfall and only a
10-30% chance of gusts over 35 mph.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 207 AM MDT Thu Sep 4 2025

High pressure remains in place over the area with the ridge axis
over Idaho, though high pressure has weakened considerably and
will continue to break down or weaken. Expect mostly partly
cloudy skies today and tomorrow with overall light winds (gusts
up to 15 to 20 mph in the afternoon).

Today will be the last day, for at least the next week, with
daytime high temperatures in the 80s and low 90s. Expect
temperatures to drop tomorrow, Friday, into the 70s and 80s
across the area with weakening high pressure and increased
cloud cover.

There is still some lingering valley smoke/haze (AQI in the low
50s) across southeast Idaho with light smoke moving into the
area over the Montana Divide with high pressure continuing to
break down. Expect air quality to improve this weekend with the
return of precipitation.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 1238 PM MDT Wed Sep 3 2025

A pattern change still looks to be on track for our long term
forecast for Eastern Idaho. By Friday afternoon, the ridge of high
pressure over our area is beginning to be pushed a bit farther east
as an area of low pressure moves into the Pacific Northwest. This
will open the door for a few isolated showers and storms on Friday.
A shortwave ejecting off of that area of low pressure will move
through the ridge over the weekend and bring some scattered showers
and storms with it. This will help cool down temperatures a few
degrees with highs on Friday in the low to mid 80s and falling into
the mid 70s to near 80 degrees for Saturday and Sunday. Storms on
Saturday and Sunday are more likely to produce some measurable
rain with an area-wide 30 to 50 percent chance of at least a
tenth of an inch of QPF from Saturday evening to Sunday evening.
Models are showing a slightly slow-down in the moisture
arriving this weekend compared to previous runs. They are also
showing a speed-up for our next system next week. While models
had been showing a Thursday/Friday arrival, ensemble clusters
now showing about a 50 percent chance of the influence of low
pressure over Idaho as early as Tuesday. So while it looked like
we would have more of a break between rounds of precipitation
this weekend and next week, that break may be much shorter. We
will have to see how models continue to handle this over the
next few days.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 507 AM MDT Thu Sep 4 2025

Expect VFR conditions with mostly mid to upper level clouds
through most of the period as well as overall light winds under
mostly high pressure. With monsoon moisture moving into the area
combined with heating, isolated showers and thunderstorms are
possible today as high pressure breaks down. Several Hi-Res
models show thunderstorms developing in the Central mountains
and moving south into the Snake plain. SUN has the best chance
of gusty outflows of up to around 30 to 35 mph but its low a
chance, 10 to 20 percent. PIH and BYI have a low chance, around
10 percent, of getting outflows as well. Have held off putting
any thunderstorms and outflows in TAFs as chances are so low.

&&

.FIRE WEATHER...
Issued at 207 AM MDT Thu Sep 4 2025

Hot and mostly dry conditions will continue today and, to a
lesser degree, Friday. Isolated (mostly dry) storm chances do
return to the forecast today and tomorrow afternoon with
increasing monsoon moisture, weakening high pressure, and
increased instability. This increase in monsoon moisture will
bring afternoon min RHs to around 12 to 20 percent today and 20
to 25 percent on Friday. These isolated storms are most likely
in Fire Weather Zones 410, 413, 422, and 425 today and in Zones
413 and 427 on Friday. Look for storm outflows of 30 to 35 mph
today and Friday. Showers and storms become more scattered on
Saturday and Sunday with an increasing chance for a wetting rain
through the weekend. The NBM continues to show an area-wide 30
to 50 percent chance of at least a tenth of an inch of QPF from
Saturday evening to Sunday evening.

Models continue to show below normal temperatures and above
normal precipiation chances next week with an upper level low
moving over the area and impacting our area for multiple days.
This is supported by most model members in the WPC model
clusters product next Tuesday through next Friday. &&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Keyes
SHORT TERM...TW
LONG TERM...AMM
AVIATION...TW
FIRE WEATHER...TW